U.S. Pat. No. 4,026,680 addresses the problem of cold zones which are formed in the pressure vessels of PSA plants, particularly large scale PSA plants for the production of oxygen from feed air where the adsorbent material used is a zeolite molecular sieve.
U.S. Pat. No. 4,026,680 discloses that temperature drops in the order of 100.degree. F. below feed air temperature have been observed at the inlet end of pressure vessels forming part of a PSA plant for the production of oxygen from feed air. Since the molecular sieve material is usually selected to operate best, as regards oxygen recovery efficiency, at ambient conditions, the effect of a cold zone is to reduce the performance of the molecular sieve material.
In order to meet this problem U.S. Pat. No. 4,026,680 teaches the transference of heat within the pressure vessel from the ambient temperature zones to the cold zone by metal solid conduction. The metal solid conduction can take the form of a plurality of metal plates positioned parallel and equidistant from each other and extending through the adsorbent bed such that heat from ambient temperature areas of the pressure vessel is conducted via the metal plates to a cold zone adjacent the inlet to the pressure vessel. In other words, the U.S. Pat. No. 4,026,680 concentrates on warming up the bed of adsorbent material at a location adjacent the inlet of the pressure vessel.